fix: correct contributor-facing README docs

[immanuwell]

Summary

Fix a small docs papercut in contributor facing READMEs.
The README template had busted comment markup plus a typo, and testing-integration/README.md opened with a broken sentence. Pretty small fix, but it cleans up stuff people actually read and copy.

Repro:

• git show origin/master:example-readme-template.md.txt | sed -n '10,20p'
• git show origin/master:testing-integration/README.md | sed -n '1,5p'

Example(s) affected

• example-readme-template.md.txt
• testing-integration

Validation

git diff --check

(no output)

rg -n "exampleas|infrastucture|If deploys" example-readme-template.md.txt testing-integration/README.md

(no output)

Checklist

• No hardcoded credentials or secrets
• No Pulumi.*.yaml stack config files included

[github-actions]

PR is now waiting for a maintainer to run the acceptance tests.
Note for the maintainer: To run the acceptance tests, please comment /run-example-tests on the PR